The invention concerns a probe for attaching at certain times to the tool spindle of a machine tool.
Probes of this kind are known for example from European Patent Specification 0 108 521. They have a stylus which is attached in a resiliently deflectable manner and activates a measuring contact device when it touches a workpiece and is therefore deflected out of its position of rest. In the course of a machining operation, various tools are attached one after the other to the spindle. The latter xe2x80x9cgrabsxe2x80x9d these automatically from a tool magazine. At the end of the machining operation, or after certain machining phases, a control measurement of the workpiece is carried out automatically with the probe. For this purpose, the probe, which likewise assumes a place in the tool magazine, is fitted onto the spindle instead of a tool. The electrical measuring signal produced by deflection of the stylus when it touches the workpiece is transmitted by means of a transmission channel from the housing of the probe to a receiving and evaluating device fastened on the machine framework. The transmission channel may be an infrared light link, a radio link, an inductive transmission device or the like.
The probe is generally supplied with energy via a battery, which is accommodated in the probe housing.
Maintaining the operating state of the transmission channel requires constant energy consumption, which in view of the restricted space and weight conditions in the probe housing should be kept as low as possible. For this purpose, it is known per se to keep the transmission channel in an inoperative, switched-off state or power-saving sleeping state during machining operation and to activate it only for the limited measuring time. The latter is achieved by acting on the probe from outside, for example by means of a further infrared link or by means of a switching device which is activated when the probe is placed against the tool spindle or thereafter via the tool spindle.
The invention, on the other hand, is concerned with an autonomous device for activating the transmission channel which is accommodated in the probe housing and is not externally controlled. It is known from the cited European patent to use a centrifugal switch or rotary acceleration sensor which responds to the rotational movement of the spindle when the probe is attached to the spindle, its housing axis being aligned with the spindle axis.
It is disadvantageous in this case that the switches or sensors of this activation device can in principle respond not only when there are pure rotational movements about the center axis of the housing but also when there are other intermittent movements, which occur when the probe is being transported between the magazine and the measuring location. It is therefore necessary to make the restoring resilient forces of the inert mass of this switch relatively great, so that the switch responds only when the spindle reaches high rotational speeds or is strongly accelerated or decelerated. This precondition for satisfactory functioning of the known activation device on the one hand prolongs the operating time of the transmission channel, and acts counter to the power-saving effect, and on the other hand prolongs the measuring cycle to the detriment of the overall piece time for machining the workpiece.
The invention is based on the object of specifying measures by which the operating time of the transmission channel can be shortened and can be better adapted to the time period required for carrying out the measuring operation.
The invention is based on a probe for attaching at certain times to the tool spindle of a machine tool, which probe comprises a housing, a stylus which is mounted on the housing, an electronic assembly which is arranged in the housing, is supplied from a power source and generates a measuring signal when the stylus is deflected out of the position of rest and also a switching device which switches, for example, in dependence on a movement and/or position of the probe and by which it is possible in interaction with the electronic assembly to activate or deactivate a transmission channel via which the measuring signal can be transmitted to a receiving and evaluating device of the machine tool. The essential idea of the invention is consequently that the electronic assembly is designed for keeping a control check on the switching device from when it reaches its switching position with respect to continuance of the switching position and for triggering the activation or deactivation of the transmission channel if the switching position continues uninterruptedly for the duration of a predetermined interrogation time. The electronic assembly proposed and described by its functional features has the consequence that a more sensitive switching device can be used and nevertheless erroneous signals as a consequence of intermittent transporting movements of the probe are avoided. The interrogation time may be, for example, one or two seconds. On account of the higher sensitivity of the switching device, it is possible for example for the spindle speed or the spindle acceleration for triggering the activation signal to be lower than previously. Depending on which position the switching device is in -to reach the switching position, i.e. in the active measuring position or in the inactive parking position, the continuance of the switching position is either a trigger for the activation or deactivation of the transmission channel. What is decisive, however, for both possibilities is the xe2x80x9cverifying time periodxe2x80x9d, in which the switching device must assume the switching position without interruption.
In a development of the invention it is advantageous to use as the switching device an inclination switch, which assumes its switching position within a specific range of inclination positions of the probe with respect to a transverse axis. Consequently, the event which triggers the activation or deactivation signal is in this case not a movement but an assumption by the probe of a position inclined in a defined state with respect to a transverse axis of the probe housing. The, for example, brief pausing in an activation position during the transporting movement from the tool magazine to the measuring location requires a significantly smaller amount of time to be expended than the acceleration up to a specific rotational speed and subsequent braking, as is the case for example when the probe is activated by a centrifugal switch. Inclination switches are advantageous in particular whenever the probe and the machine tools are kept in a magazine which is rotationally mounted (turret magazine). The decisive range of inclination positions for activating the transmission channel may comprise, for example in the case of a vertical tool spindle, the vertical position of the probe with downwardly pointing stylus and the positions deviating from this by a few angular degrees.
Preferably suitable as an inclination switch is a liquid switch, in particular a mercury switch. The switch vessel receiving the liquid may consist of a conductive or nonconductive material and have electrodes designed according to requirements.
In a further particularly advantageous embodiment of the invention, the stylus with a measuring contact device for sensing a stylus deflection forms the switching device, the electronic assembly being designed for deactivating the transmission channel when the measuring contact device senses a deflection of the stylus which continues uninterruptedly for longer than a predetermined period of time.
This accordingly dispenses with a separate switching device for the deactivation of the transmission channel. Rather, the already existing stylus with a measuring contact device assumes this function. This must be imagined by envisaging that the stylus of the probe is accommodated at its storage location for example in such a way that the stylus is constantly deflected. That is to say, as soon as the probe reaches the storage location, the stylus of the probe is deflected by suitable means, whereby the transmission channel switches off after a predetermined interrogation time.
The electronic assembly is preferably designed for activating the transmission channel as soon as the measuring contact switch detects no deflection of the stylus. That is to say the transmission channel switches on at the moment at which the probe is removed from its storage place.